Field of the Invention
The invention relates to a method and a device for joining the ends of sheets, with two or more surfaces arranged flat on top of each other, more particularly metal strips that can be coiled, in order to draw these successively through a treatment or machining system.
Description of Related Art
Metal sheets that can be coiled (strips or foils) are, in the most varied of treatment or machining processes, initially coiled and subsequently recoiled. This takes place for example in rolling mills, in annealing furnaces, in degreasing lines, in cleaning lines, in pickling lines, in coating lines, in stretching installations or similar. The sheets are supplied in the wound form, as a so-called coil, unwound in the input area in order to pass through the system and, following processing, at the end of the system rewound to form a coil again.
If the coil on the input side comes to an end, it is necessary to join the end of this with the start section of a fresh coil, which is then also drawn through the various processing points in the system by the strip end already in the system as it continues passing through. Since this usually takes place in a continuous process, the join must be created in the shortest time possible, since the systems frequently have only a relatively small strip store and a system standstill is to be avoided.
EP 0 029 415 A2 discloses how to create an interlocking connection between the ends of strips, wherein by means of piercing punches in the overlapping area a number of cruciform cuts are created and the resultant flaps between two cross-shaped incisions provided with two-layer flanging. This leads to four-layer connection points and thus, in particular when punching cross-shaped incisions, to relatively rigid strip sections which are not readily able to pass through all systems.
It has therefore also previously been proposed (DE 199 59 090 A1), to provide the overlapping ends of two metal sheets with ring-shaped welded joints at a distance from the ends of the sheets. This results in the merging of the strip material in the area of the holes, creating the required stability.
A further known device (GB-PS 291 684) serves to join the ends of thin foil sheets, for example of aluminium foil. Here, in the overlapping area of the sheet ends, a roller provided with a plurality of electrodes is lowered onto the sheet, wherein the electrodes in the area of a counter roller with corresponding openings pierce the sheet and by means of a voltage applied between the electrodes and the sheet the ends are electrically welded together.